Ink visible under narrow band UV radiation

ABSTRACT

An ink can be substantially invisible under most lighting conditions, and only visible when excited by UV energy having a wavelength specific to the colorant. The ink can include a liquid vehicle and a fluorescent colorant. The fluorescent colorant can have an average particle size of less than about 200 nm. Such ink can be configured as an ink-jet ink.

BACKGROUND

For some time, there has been a desire to produce systems and methodsthat can offer a greater degree of document security. For example,documents often need to be marked as original, such as identificationcards, passports, checks, and currency. Alternatively, documents mayneed to be marked with certain information that is preferably notvisible under normal lighting conditions. For this purpose, specializedwatermarks and printing techniques have been developed. Additionally, avariety of printing materials have been incorporated into suchprocesses. Counterfeiting continues to advance along with thedevelopments in providing more authentic and secure documents. Thus,there is a need to develop more techniques and materials that impart newand additional levels of authentication to documents and the like.

DETAILED DESCRIPTION

Reference will now be made to the exemplary embodiments of the presentdisclosure, both those described and those illustrated in the drawing,and specific language will be used herein to describe the same. It willnevertheless be understood that no limitation of the scope of thedisclosure is thereby intended. Alterations and further modifications ofthe inventive features illustrated herein, and additional applicationsof the principles of the disclosure as illustrated herein, which wouldoccur to one skilled in the relevant art and having possession of thisdisclosure, are to be considered within the scope of the disclosure.

In describing and claiming the present disclosure, the followingterminology will be used.

The singular forms “a,” “an,” and “the” include plural referents unlessthe context clearly dictates otherwise. Thus, for example, reference to“a colorant” includes reference to one or more colorants.

The term “fluid” does not require that all components in the compositionbe liquid, as pigments are typically dispersed in the color-containingfluid. Thus, fluid dispersions and fluid solutions are both included ascolorant-containing fluids. It is also noted that the term “colorant” inmany embodiments includes materials that receive light outside of thevisible spectrum, and reflect light within the visible spectrum.

The term “stable” when referring to an ink or other solution in thepresent application, refers to a dispersion including a plurality ofparticles where the particles remain dispersed in solution for anextended period of time under normal storage and/or usage conditions.Such conditions may be dependent on the purpose of the solution or ink,and are thus ink-specific. Non-limiting examples of times on which tobase stability include greater than 1 week, greater than 1 month,greater than 6 months, greater than 1 year, and greater than 3 years.

As used herein, the term “hue” refers to a color within the visiblespectrum. Both “hue” and “color” are used to indicate distinct colors.Technically, two different hues are distinguished as light is emitted orreflected from one hue at a wavelength that is different from awavelength of the other hue.

The term “fluorescent colorant” as used herein, indicates a colorantthat, when exposed to a non-visible wavelength of energy, emits orreflects a visible wavelength. Furthermore, the fluorescent colorantsused herein, are substantially invisible except when exposed to theactivating non-visible wavelength of energy. Non-limiting examples offluorescent colorants include (SrCaBaMg)₅(PO₄)₃Cl:Eu, LaPO₄:Ce,LaPO₄:Tb, Y₂O₃:Eu, Ca₁₀(PO₄)₆FCl:Sb, Ca₁₀(PO₄)₆FCl:Mn, and combinationsthereof. Additional non-limiting examples of colorants includehalcogenides, e.g. MeS, MeSe; halogenides, e.g. BaFCl; oxides, e.g.Y₂O₃, La₂O₃, Gd₂O₃, CaYBO₄, ScBO₂, YBO₃, LaBO₃, BaBO₃, CeBO₃, BaB₂O₄;fluorides, e.g. CaF₂, SrF₂, BaF₂, (LaAlCe)F₃; borates; aluminates, e.g.YAl₃B₄O₁₂, Y₃Al₅O₁₂, Y₄Al₂O₉; silicates, e.g. Sc₂Si₂O₇, Y₂SiO₅,Ce₂Si₂O₇; phosphates, e.g. YPO₄, LaPO₄, CePO₄, GdPO₄; vanadates, e.g.YVO₄, GdVO4; aluminum yttrium garnets; gallium gadolinium garnets;oxihalides, e.g. YOCl, LaOCl, LaOBr; oxisulphades, e.g. Y₂O₂S; halc andeven more complicated materials like lantanum stabilized a-SiAlON,particularly LaAl(Si_(6-z)Al_(z))N_(10-z)O_(z):Ce³⁺ (for z=1 excitationat 350±100 nm, emission at 500±10 nm); similar materials and othercombinations of noted materials.

The term “dopant” in relation to the colorant, refers to a materialincluded with the fluorescent colorant which at least slightly altersthe properties of the colorant. An atomic structure of doping elementsshould have excitation states relaxed to ground (main) statecorresponding to visible light range. Typically all lantanoids withf-orbitals and d-transition metals like Cu, Ti, etc. satisfy theseconditions. Concentration of a dopant may vary from 0 to about 1 atomic%. At high concentration of the dopant, energy coupling decreasesintensity and increases emission band. Dopant material is typicallyindicated after a colon. For example, Y₂O₃:Eu is yttrium oxide dopedwith europium. Dopants can be used to shift and narrow excitation bandphosphors.

“UV” or “ultra violet” is defined as radiation with a wavelength rangingfrom about 10 nm to about 400 nm. UV radiation can be sub-divided intolong wave or “blacklight” (about 315 nm to about or slightly greaterthan 380 nm), medium wave (about 280 to about 315 nm), and short wave(less than about 280 nm). Often, UV radiation can be utilized inaccordance with embodiments of the present disclosure such that it ismatched to the narrow range of fluorescence of a given fluorescentcolorant. Thus, in one embodiment, by matching a narrow range of UVenergy to a narrow range of fluorescing that occurs for a givencolorant, an original document may be able to be authenticated, orprovide some other benefit.

Additionally, as discussed herein, exposing a printed image or printedink to UV radiation is meant to indicate exposure at a greater level tothe UV radiation than is typically found in ambient light. For example,bringing the colorants or media near an energy source that emits UVlight of the noted region is included in exposing the image to UVradiation. For example, taking the image or media into the sunlight orambient light is not considered exposing the image or media to UVradiation having a wavelength of about 200 nm to about 280 nm, eventhough sunlight or ambient light includes such UV radiation.

The ink, and particularly the fluorescent colorant, e.g. yttrium oxidedoped with europium (Y₂O₃:Eu), is said to absorb UV radiation and shiftthe wavelength of the UV radiation to a reflected visible wavelength.Although this is the terminology used to explain the phenomena ofexciting the fluorescent colorant with UV energy and having thefluorescent colorant emit a visible wavelength, it is understood thatother explanations or descriptions are equally as probable and/or validso long as it indicates that the fluorescent colorant receives UVwavelength and, as a result, emits or reflects visible wavelengthenergy. For example, it could be said that the fluorescent colorantabsorb non-visible radiation and emit a visible wavelength. Further, thefluorescent colorant could be said to fluoresce a visible color uponreceiving a non-visible radiation.

The terms “light” and “radiation” can be used interchangeably and meanenergy in the form of electromagnetic waves.

As used herein, the term “about” is used to provide flexibility to anumerical range endpoint by providing that a given value may be “alittle above” or “a little below” the endpoint. The degree offlexibility of this term can be dictated by the particular variable andwould be within the knowledge of those skilled in the art to determinebased on experience and the associated description herein.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Numerical data may be expressed or presented herein in a range format.It is to be understood that such a range format is used merely forconvenience and brevity and thus should be interpreted flexibly toinclude not only the numerical values explicitly recited as the limitsof the range, but also to include all the individual numerical values orsub-ranges encompassed within that range as if each numerical value andsub-range is explicitly recited. As an illustration, a numerical rangeof “about 1 to about 5” should be interpreted to include not only theexplicitly recited values of about 1 to about 5, but also includeindividual values and sub-ranges within the indicated range. Thus,included in this numerical range are individual values such as 2, 3, and4 and sub-ranges such as from 1-3, from 2-4, and from 3-5, etc. Thissame principle applies to ranges reciting only one numerical value.Furthermore, such an interpretation should apply regardless of thebreadth of the range or the characteristics being described.

According to various aspects of the present disclosure, an ink-jet ink,or a component thereof, can be substantially invisible under themajority of lighting and reproducing conditions. Such ink can be visibleunder a narrow band of energy. Specifically, the ink, or a componentthereof, when printed on a media substrate, can be substantiallyinvisible, meaning that under typical lighting circumstances, the ink orcomponent will be invisible, or near to invisible to the unaided eye,except when excited by UV energy having a wavelength in a narrow rangethat is matched to the fluorescing range of a given colorant. Aspreviously mentioned, exposing a printed image or printed ink to UVradiation of the noted specific range is meant to indicate exposure at agreater level to the UV radiation than is typically found in ambientlight. Examples of this include bringing the colorants or media near anenergy source that emits UV light of the noted region is included inexposing the image to UV radiation, or taking the image or media intothe sunlight or ambient light is not considered exposing the image ormedia to UV radiation having a wavelength of about 200 nm to about 280nm, even though sunlight or ambient light includes such UV radiation.When the ink-jet ink is exposed to adequate amounts radiation of thenoted range which is more intense than is present in ambient light, itemits a red hue that is visible to the eye. Therefore, to verify themark is present, or to view the printed image, a UV source that emits UVradiation having a wavelength of about 200 nm to about 280 nm would bedirected to the printed ink, at which point a visible image would bevisible to the eye. Such visible state is not permanent, and the imagewould remain visible only as long as activated by the necessary UVradiation. In one embodiment, a method or system may include the use orpresence of a UV energy source that emits UV radiation only within thefluorescing range of the fluorescent colorant. The ink can include oneor more fluorescent colorants. Such colorants are substantiallyinsoluble in water, however, can form stable solutions and inks, basedon careful selection of particle size, along with other ink components.Non-limiting examples of fluorescent colorants include(SrCaBaMg)₅(PO₄)₃Cl:Eu, LaPO₄:Ce, LaPO₄:Tb, Y₂O₃:Eu, Ca₁₀(PO₄)₆FCl:Sb,Ca₁₀(PO₄)₆FCl:Mn, and combinations thereof.

In one embodiment, the fluorescent colorant can comprise or consistessentially of YVO₄:Sm³⁺, emitting at about 600 nm and about 650 nm;YVO₄:Eu³⁺, emitting at about 610 nm; YPO₄:Tb³⁺, emitting at about 545nm; YVO₄:Dy³⁺, emitting at about 570 nm; YVO₄:Ho³⁺, emitting at about545 nm and at about 570 nm; YVO₄:Er³⁺, emitting at about 550 nm; andYVO₄:Tm³⁺, emitting at about 475 nm. Additionally, dopants can be usedwith Y₂O₃. Inclusion of differing dopants can alter the excitation andemission peaks for each colorant. Non-limiting examples of dopants andrelated excitation and emission peaks include (with lower peaksindicating excitation, and higher peaks representing emission, and withprimary peaks reported): Pr, 283 nm, 619 nm, 630 nm; Sm, 407 nm, 608 nm;Eu, 253 nm, 611 nm; Tb, 280 nm, 304 nm, 543.5 nm; Dy, 231 nm, 349.5 nm,572.5 nm; Er, 380 nm, 563 nm; Ho, 362 nm, 448 nm, 550 nm; and Tm, 362nm, 453 nm. Measurements represent a concentration of 0.1 mol % ofdopant except for Er3+, which represents a 1 mol % concentration.

In a specific embodiment, the fluorescent colorant can comprise orconsist of Y₂O₃:Eu. The fluorescent colorant can be present in anyamount that can produce, when printed and exposed to appropriatenon-visible energy, a visible image. In a specific embodiment, thefluorescent colorant can be present in a liquid vehicle at an amountfrom about 0.1 wt % to 3 wt %. The liquid vehicle can be aqueous ornon-aqueous. The fluorescent colorant can have an average particle sizeof less than about 200 nm.

In accordance with the difficulties outlined, various details areprovided herein which are applicable to each of the ink-jet ink, method,security marking, etc., and methods for making the same. Thus,discussion of one specific embodiment is related to and provides supportfor this discussion in the context of the other related embodiments.Additionally, for ease of discussion, the fluorescent colorant Y₂O₃:Eumay be used exclusively in discussion. The use of the noted colorant isnot to be taken as applications wherein only that colorant would work,rather the Y₂O₃:Eu could, and should, be replace interchangeably withany fluorescent colorant having the requirements as outlined above.Therefore, discussion of Y₂O₃:Eu and response to UV energy having awavelength range of from about 200 nm to about 280 nm, is not to betaken as directed to Y₂O₃:Eu only, but teaches each fluorescent coloranthaving a particle size of less than 200 nm, capable of forming a stablesolution, and responsive to energy in the form of a narrow range, inconjunction with the fluorescent colorants responsive narrow range.

Specifically, an ink jet ink can comprise a liquid vehicle, and afluorescent colorant in the form of substantially insoluble particleshaving an average particle size of less than about 200 nm. The ink-jetink can be configured such that, when printed on a media substrate, theportion of the fluorescent colorant in the ink jet ink can produce avisible image that is substantially invisible except when excited by aspecific UV energy having a range of not greater than about 80 nm andspecific to the fluorescent colorant. In a further embodiment, the inkjet ink can be substantially free of other non-fluorescent coloringagents. In the case of Y₂O₃:Eu, the fluorescent colorant portion of theink-jet ink can be substantially invisible except when excited by UVenergy having a wavelength from about 200 nm to about 280 nm.

In another embodiment, a method of making an ink-jet ink can compriseblending a fluorescent colorant having a particle size of less than 200nm to create a dispersion, and blending from about 1 wt % to about 5 wt% of the dispersion with a liquid vehicle to form a stable ink. In aspecific embodiment, the dispersion can have a pH of about 6 to about 7.

In another embodiment, a method of printing and illuminating aselectively-visual image can comprise printing an ink on a mediasubstrate, wherein the ink includes a liquid vehicle and Y₂O₃:Eu.Another step includes exposing the printed image to UV energy having awavelength from about 200 nm to about 280 nm. The Y₂O₃:Eu can have anaverage particle size of less than about 200 nm, and the ink can besubstantially free of other non-fluorescent agents. When the ink isprinted on a media substrate, the ink or the fluorescent colorantportion can be substantially invisible except when excited by UV energyhaving a wavelength in the range corresponding to the fluorescentcolorant. In one embodiment, though not required, UV energy can be usedthat is only within the fluorescing range of the colorant. In thismanner, document authentication may occur.

In still another embodiment, a security marking can comprise an imageincluding 0.1 μg/cm² to 50 μg/cm² Y₂O₃:Eu, wherein the Y₂O₃:Eu has anaverage particle size of less than about 200 nm. In a furtherembodiment, a security marking can comprise an image including 0.1μg/cm² to 5 μg/cm² Y₂O₃:Eu, wherein the Y₂O₃:Eu has an average particlesize of less than about 200 nm. These images can be substantially freeof other photoluminescent agents, and the security markings can also besubstantially invisible except when excited by UV energy having awavelength from about 200 nm to about 280 nm.

Y₂O₃:Eu can provide the highly-selective visual marking of the ink,meaning an ink, including yttrium oxide doped with europium is visibleonly under select circumstances, i.e. when exposed to radiation of about200 nm to about 280 nm. To create an image, the Y₂O₃:Eu can be includedin a variety of vehicles or used in various ways. In a particularembodiment, inks and/or liquid toners having Y₂O₃:Eu which is capable ofabsorbing non-visible radiation of a narrow band and shifting thewavelength to a reflected visible wavelength can be applied to some typeof media, e.g., coated media sheets, transparencies, etc. One method ofapplying the colorant-containing fluids to media can be ink-jetprinting. The Y₂O₃:Eu is substantially invisible under many lightingconditions because of the relative emission intensities. Emissionintensity is roughly 100 times greater for Y₂O₃:Eu when excited withradiation having a wavelength of about 254 nm as compared to Y₂O₃:Euwhen excited with radiation having a wavelength of about 365 nm. Thisunique property of Y₂O₃:Eu accounts for the ink being substantiallyinvisible under lighting conditions outside of the narrow range of about200 nm to about 280 nm. Normal lighting, e.g. office lighting,conditions does not supply the intensity of UV radiation in the 200 nmto 280 nm range sufficient to cause the Y₂O₃:Eu to shift the wavelengthto a reflected visible wavelength that is significantly detectable tothe naked eye. Thus the Y₂O₃:Eu can be used to produce an ink that issubstantially invisible except when subjected to UV radiation of anarrow band.

To improve the qualities of the ink, both ink performancecharacteristics, and printed image quality, the fluorescent colorant,e.g. Y₂O₃:Eu, can have an average particle size of less than about 200nm. In a more detailed embodiment, the average particle size can be lessthan about 150 nm. In still a further detailed embodiment, the averageparticle size can be less than about 100 nm. Such particle sizes,depending on other components in the inks, allow for the creation ofstable inks. The concentration of europium in yttrium oxide is typicallymeasured in mole percent. As such, the Y₂O₃:Eu of the presentapplication can have a concentration of europium in yttrium oxide fromabout 1 mole percent to about 3 mole percent. In a further embodiment,the concentration of europium in yttrium oxide can be about 2 molepercent.

In some cases, it may be beneficial to use Y₂O₃:Eu of a smaller particlesize. For example, the potential use of the ink, ink additives, etc.,may, in some cases, work well with Y₂O₃:Eu of smaller particle size.Therefore, in one aspect, the average particle size of the Y₂O₃:Eu canbe less than about 150 nm. In a more specific aspect, the Y₂O₃:Eu canhave an average particle size of less than about 100 nm.

The Y₂O₃:Eu described herein can be utilized to produce images that areactivated by specific non-visible radiation. Accordingly, a method forprinting a selectively-visual image can include printing an ink of thepresent disclosure on a media substrate. The ink can include an aqueousliquid vehicle and yttrium oxide doped with europium. The Y₂O₃:Eu can bepresent at about 0.1 wt % to 3 wt % and can have an average particlesize of less than about 200 nm. The ink can be substantially free ofother non-fluorescent coloring agents. Therefore, the printed ink can besubstantially invisible except when excited by UV energy having awavelength from about 200 nm to about 280 nm. The method can furtherinclude exposing the printed image to UV energy having a wavelength fromabout 200 nm to about 280 nm. In an embodiment, the method of printingcan include ink jetting an ink on a media substrate.

In one embodiment, the ink can include Y₂O₃:Eu as the only coloringagent. In such cases, the non-Y₂O₃:Eu coloring agents of the presentdisclosure that are excluded from the ink formulation can include anystandard or non-standard type of coloring agent not excluding dyes andpigments. Further, such coloring agents can be activated with visible ornon-visible radiation, i.e. UV or IR, and can include colorants such as,fluorescent colorants, phosphorescent colorants, etc. In anotherembodiment, the ink can include non-Y₂O₃:Eu coloring agents, includingany of the above-noted types of coloring agents.

Regarding the liquid vehicle that is present in some embodiments, in oneaspect, the vehicle can be aqueous or can be non-aqueous. In oneembodiment, the vehicle can include at least one co-solvent. Suchco-solvent can be present in the liquid vehicle at about 1 wt % to about50 wt %. In a more specific embodiment, the co-solvent can be present atabout 1 wt % to about 50 wt %, and more typically, from about 1 wt % toabout 20 wt %.

Classes of co-solvents that can be used separately or in combinationinclude aliphatic alcohols, aromatic alcohols, diols, glycol ethers,polyglycol ethers, caprolactams, formamides, acetamides, and long chainalcohols. Examples of such compounds include primary aliphatic alcohols,secondary aliphatic alcohols, 1,2-alcohols, 1,3-alcohols, 1,5-alcohols,ethylene glycol alkyl ethers, propylene glycol alkyl ethers, higherhomologues of polyethylene glycol alkyl ethers, N-alkyl caprolactams,unsubstituted caprolactams, both substituted and unsubstitutedformamides, both substituted and unsubstituted acetamides, and the like.Specific examples of co-solvents that can be used includetrimethylolpropane, 2-pyrrolidone, and 1,5-pentanediol. In a specificembodiment, the co-solvent can comprise or consist essentially of2-pyrrolidone.

The liquid vehicle can include one or more surfactants. Specifically,the liquid vehicle can include one or more non-ionic, cationic, and/oranionic surfactants, and if present, can be included at from about 0.01wt % to about 5.0 wt %. One or more of many surfactants can be used asare known by those skilled in the art of ink formulation and may includealkyl polyethylene oxides, alkyl phenyl polyethylene oxides,polyethylene oxide block copolymers, acetylenic polyethylene oxides,polyethylene oxide (di)esters, polyethylene oxide amines, protonatedpolyethylene oxide amines, protonated polyethylene oxide amides,dimethicone copolyols, substituted amine oxides, and the like.Non-limiting examples of surfactants that can be used include primary,secondary, and tertiary amine salt compounds such as hydrochloric acidsalts, acetic acid salts of laurylamine, coconut amine, stearylamine,rosin amine; quaternary ammonium salt type compounds such aslauryltrimethylammonium chloride, cetyltrimethylammonium chloride,benzyltributylammonium chloride, benzalkonium chloride, etc.; pyridiniumsalty type compounds such as cetylpyridinium chloride, cetylpyridiniumbromide, etc.; nonionic surfactant such as polyoxyethylene alkyl ethers,polyoxyethylene alkyl esters, acetylene alcohols, acetylene glycols; andother surfactants such as 2-heptadecenyl-hydroxyethylimidazoline,dihydroxyethylstearylamine, stearyldimethylbetaine, andlauryldihydroxyethylbetaine; and combinations thereof. Fluorosurfactantscan also be used such as those previously known in the art.

Other ink components known in the art such as biocides, viscositymodifiers, materials for pH adjustment, sequestering agents,preservatives, latexes, polymers, and the like, can also be present.Regarding the other additives that can be included in the liquid vehicleformulations, it is understood that the enumerated components areexemplary and do not limit the scope of vehicle components that can beused. For example, in some embodiments of the present disclosure, it maybe favorable for the liquid vehicle to comprise water-soluble organicsolvents or other co-solvents, and other additives as part of the liquidmedium. The balance of any embodiment formulation can be purified water,or other vehicle component known in the art.

Consistent with the formulation of this disclosure, various otheradditives may be employed to optimize the properties of the inkcomposition for specific applications. Examples of these additives arethose added to inhibit the growth of harmful microorganisms. Theseadditives may be biocides, fungicides, and other microbial agents, whichare routinely used in ink formulations.

Sequestering agents such as EDTA (ethylene diamine tetra acetic acid)may be included to eliminate the deleterious effects of heavy metalimpurities, and buffer solutions may be used to control the pH of theink. From 0.001% to 2.0% by weight, for example, of either of thesecomponents can be used. Viscosity modifiers and buffers may also bepresent, as well as other additives known to those skilled in the art tomodify properties of the ink as desired. Such additives can be presentat from 0.01% to 20% by weight.

Additionally, the liquid vehicle can comprise humectants. Humectants canbe present to enhance the longevity of solution and solubilitycharacteristics, which can be maintained by retention of moisture withinthe liquid vehicle. Examples of humectants include, but are not limitedto, nitrogen-containing compounds such as urea, thiourea, ethylene urea,alkylurea, alkylthiourea, dialkylurea, dialkylthiourea; sugars such as1-deoxy-D-galactitol, mannitol, and inositol, and combinations thereof.

The liquid vehicle can also comprise solution characteristic modifierssuch as viscosity modifiers, pH adjusters, preservatives, various typesof antioxidants, and evaporation accelerators. pH adjustors that can beused comprise base agents such as sodium hydroxide, lithium hydroxide,sodium carbonate, ammonium carbonate ammonia sodium acetate, ammoniumacetate, morpholine, monoethanolamine, diethanolamine, triethanolamine,ethylmonoethanolamine, n-butyldiethanolamine, di-n-butylethanolamine,monoisopropanolamine, diisopropanolamine, and triisopropanolamine, andthe like as well as combinations thereof. Additionally, pH adjustors canalso comprise acidic agents that can be selected from the list of acidiccrashing agents.

Additionally, solids (either dissolved in the liquid vehicle ordispersed therein) can also be present in the formulations of thepresent disclosure, and can include binders, other latex particulates,plasticizers, etc.

Media substrates can be any base material that can be plain or coatedand is configured to receive ink in accordance with an embodiment of thepresent disclosure. A non-limiting example of a media substrate ispaper. Such paper or other media substrates can be coated substrates,such as polymeric coated substrates, swellable media, or micro-porousmedia. In the example of paper, the paper can in some embodiments bephoto paper, and can have a surface finish such as gloss, matte, orsemi-gloss.

In one embodiment, the security marking can be on a media substrate. Inone aspect, when the image is excited with UV energy having a wavelengthfrom about 200 nm to about 280 nm, e.g. about 254 nm, the image canreflect a red hue. Such reflected hue, in one embodiment, can be a verynarrow emission peak.

Many counterfeiting and duplication involves the use of consumer ownedscanning and/or copy equipment. The inks of the present application canbe used to create security markings wherein the image is not detectablewith a consumer-marketed scanner or copy machine. Such images can beextremely useful as they can greatly reduce the level of counterfeiting.Furthermore, such images can be difficult to detect because the imagewould have to be exposed to not just UV light, but to a narrow andspecific range of UV light, and therefore, may be overlooked by would-becounterfeiters. Many scanner and copy machines will typically causevisible emission for compounds that excite at wavelengths below about400 nm. For colorants that excite below this threshold, a visibleindication of presence would not appear when copied or scanned undernormal circumstances. Such is the case with Y₂O₃:Eu, which excites at awavelength far below the 400 nm threshold.

Under some circumstances, a UV light source may provide effectiveamounts of UV radiation, e.g. in the about 200 nm to about 280 nm range,as part of radiation of a broad range. Applications of this technologydo not end with security, though. Printing and the resulting images ofthis type can be used to produce unique versions of any printedmaterial. In one aspect, the image can be used as a game or part of agame, such as a game piece (e.g. with secret decoding aspects). Further,such images can be useful in décor as with posters and artwork.

Inks and security markings according to the present disclosure aresubstantially invisible except when excited by UV energy having awavelength corresponding to an excitation wavelength for the colorant.In one non-limiting example, the wavelength can be from about 200 nm toabout 280 nm. In a specific embodiment, the UV energy can have awavelength from about 240 to about 265 nm. Excitement in the range of200 nm to 280 nm can produce a narrow emission peak, which can allow foradditional levels of security, particularly when combined with spectralreaders to verify the security marking.

EXAMPLES

The following examples illustrate embodiments of the disclosure that arepresently known. Thus, these examples should not be considered aslimitations of the present disclosure, but are merely in place to teachhow to make the best-known compositions of the present disclosure basedupon current experimental data. As such, a representative number ofcompositions and their method of manufacture are disclosed herein.

Example 1 Preparation of Y₂O₃:Eu Dispersion

4 g of Y₂O₃:Eu is ground in a media mill for 2 hours in 100 mL of waterat a pH of 6.7. At the end of milling, the Y₂O₃:Eu has an averageparticle size of less than 200 nm. This particle size can be confirmedby laser diffraction particle size analysis.

Example 2 Preparation Of Ink Jet Ink

2 wt % of the dispersion of Example 1 is blended into an aqueous mixturewith 8 wt % 2-pyrrolidone and 0.05 wt % surfactant to form a stable(i.e. shelf-stable over a period of time consistent with industrystandards) ink-jet ink.

Example 3 Fluorescence Of Ink-Jet Ink

The ink-jet ink of Example 2 is printed on a media substrate. Underambient light, the ink-jet ink is substantially invisible. Uponirradiation with UV energy ranging from 200 nm to 280 nm, the ink-jetink is illuminated and becomes humanly visible.

While the disclosure has been described with reference to certainpreferred embodiments, those skilled in the art will appreciate thatvarious modifications, changes, omissions, and substitutions can be madewithout departing from the spirit of the disclosure. It is thereforeintended that the disclosure be limited only by the scope of theappended claims.

What is claimed is:
 1. A stable ink jet ink, comprising: a liquidvehicle; and a fluorescent colorant in the form of substantially waterinsoluble particles having an average particle size of less than about200 nm, wherein when the ink jet ink is printed on a media substrate,the fluorescent colorant in the ink jet ink is substantially invisibleexcept when excited within a narrow range UV energy that is specific tothe fluorescent colorant, the narrow range being no greater than about80 nm.
 2. An ink-jet ink as in claim 1, wherein the fluorescent colorantis selected from (SrCaBaMg)₅(PO₄)₃Cl:Eu, LaPO₄:Ce, LaPO₄:Tb, Y₂O₃:Eu,Ca₁₀(PO₄)₆FCl:Sb, Ca₁₀(PO₄)₆FCl:Mn, and combinations thereof.
 3. An inkjet ink as in claim 2, wherein the fluorescent colorant includesY₂O₃:Eu, and the ink jet ink produces a visible image that issubstantially invisible except when excited by UV energy having awavelength ranging from 200 nm to 280 nm.
 4. An ink jet ink as in claim3, wherein the concentration of Eu in the Y₂O₃:Eu is from about 1 molepercent to about 3 mole percent.
 5. An ink-jet ink as in claim 3,wherein the visible image is at least 100 times greater than a visibleimage excited outside the wavelength range of 200 nm to 280 nm.
 6. Anink-jet ink as in claim 1, wherein the ink jet ink is substantially freeof other non-fluorescent coloring agents, and the ink jet ink produces avisible image that is substantially invisible except when excited by UVenergy having a wavelength ranging from 200 nm to 280 nm.
 7. An ink-jetink as in claim 1, wherein the fluorescent colorant has an averageparticle size of less than about 150 nm.
 8. An ink-jet ink as in claim1, wherein the fluorescent colorant has an average particle size of lessthan about 100 nm.
 9. A system for printing and illuminating aselectively-visual image, comprising: (a) a media substrate; (b) an inkjet ink, comprising: (i) a liquid vehicle, and (ii) a fluorescentcolorant in the form of substantially water insoluble particles havingan average particle size of less than about 200 nm, wherein when theink-jet ink is printed on the media substrate, the fluorescent colorantin the ink-jet ink is substantially invisible except when excited usinga narrow range UV energy that is specific to the fluorescent colorant,the narrow range being no greater than about 80 nm; and (c) a UV energysource configured to emit UV energy only within the narrow range.
 10. Asystem as in claim 9, wherein the fluorescent colorant is selected from(SrCaBaMg)₅(PO₄)₃Cl:Eu, LaPO₄:Ce, LaPO₄:Tb, Y₂O₃:Eu, Ca₁₀(PO₄)₆FCl:Sb,Ca₁₀(PO₄)₆FCl:Mn, and combinations thereof.
 11. A system as in claim 10,wherein the fluorescent colorant includes Y₂O₃:Eu, and the ink jet inkproduces a visible image that is substantially invisible except whenexcited by UV energy having a wavelength ranging from 200 nm to 280 nm,and wherein the UV energy source is configured to emit UV energy onlywithin the range of 200 nm to 280 nm.
 12. A system as in claim 9,wherein the ink jet ink is substantially free of other non-fluorescentcoloring agents, and the ink jet ink produces a visible image that issubstantially invisible except when excited by UV energy having awavelength ranging from 200 nm to 280 nm, and wherein the UV energysource is configured to emit UV energy only within the range of 200 nmto 280 nm.
 13. A method of printing and illuminating aselectively-visual image, comprising: (a) printing an ink on a mediasubstrate, the ink including: (i) a liquid vehicle, and (ii) afluorescent colorant in the form of substantially water insolubleparticles having an average particle size of less than about 200 nm,wherein when the ink-jet ink is printed on the media substrate, thefluorescent colorant in the ink-jet ink is substantially invisibleexcept when excited within a narrow range UV energy that is specific tothe fluorescent colorant, the narrow range being no greater than about80 nm; and (b) exposing the printed image to UV energy having awavelength that is only within the narrow range of UV energy.
 14. Amethod as in claim 13, wherein the step of printing is by ink-jetting.